Re: Bare repositories in the working tree are a security risk

From: Glen Choo <chooglen@google.com>
To: Junio C Hamano <gitster@pobox.com>
Cc: git@vger.kernel.org, Emily Shaffer <emilyshaffer@google.com>,
	justin@justinsteven.com, Taylor Blau <me@ttaylorr.com>,
	martinvonz@google.com,
	"brian m. carlson" <sandals@crustytoothpaste.net>
Subject: Re: Bare repositories in the working tree are a security risk
Date: Fri, 15 Apr 2022 15:43:15 -0700	[thread overview]
Message-ID: <kl6l8rs67yt8.fsf@chooglen-macbookpro.roam.corp.google.com> (raw)
In-Reply-To: <kl6lbkx2821q.fsf@chooglen-macbookpro.roam.corp.google.com>

Glen Choo <chooglen@google.com> writes:

> Junio C Hamano <gitster@pobox.com> writes:
>
>> Glen Choo <chooglen@google.com> writes:
>>
>>> Yes, I mean that even the current directory will be ignored when
>>> discovery is disabled.
>>
>> OK.
>>
>>>>                                                I am not sure that
>>>> is realistically feasible (I am thinking of cases like "git fetch"
>>>> going to the remote repository on the local disk that is bare to run
>>>> "git upload-pack"), but if the fallout is not too bad, it may be a
>>>> good heuristics.
>>>
>>> Good detail - I hadn't considered the impact on our own child processes.
>>> I suspect this might be a huge undertaking. Unless there is significant
>>> interest in this option, I probably won't pursue it further.
>>
>> I do not necessarily think so.  The entry points to transport on the
>> server side are quite limited (and the client side is dealing with
>> your own repositories anyway), and they already know which directory
>> in the server filesystem to hand to the upload-pack and friends, so
>> it would be a matter of passing GIT_DIR=$there when they call into the
>> run_command() API, if they are not already doing so.
>
> FWIW I experimented with turning off bare repo recognition altogether
> and seeing what breaks.
>
> CI Run: https://github.com/chooglen/git/runs/6042600953?check_suite_focus=true
>
> AFAICT, most of the test failures are what we'd expect if we stopped
> recognizing bare repos altogether. One stands out to me in particular
> though - in t5550-http-fetch-dumb.sh, 
>
>     git clone $HTTPD_URL/dumb/repo.git clone-tmpl
>
> yields 
>
>     ++ git clone http://127.0.0.1:5550/dumb/repo.git clone-tmpl
>     Cloning into 'clone-tmpl'...
>     fatal: repository 'http://127.0.0.1:5550/dumb/repo.git/' not found
>
> This sounds to me like Git isn't recognizing the static http files as a
> remote Git repo, and if so, --git-dir doesn't sound like it'll save us.
> But I'm not that familiar with the transport code so I don't know if
> this is a big deal or just a quirk with our httpd tests.

Ok I think this is a false alarm - the previous test does some setup on
the server, which is a bare repo. It was the _setup_ that was broken,
not the actual `git clone`.